In general, linear actuators are used to generate motion in a straight line. One class of linear actuator is the electromagnetic linear actuator or linear motor, one example of which is described in the earlier filed patent application, U.S. Pat. Pub. 2014/0312716, the contents of which are incorporated herein by reference. In its most basic form, the linear actuator described therein includes a linear array of coils wound around a core of magnetically permeable material and an actuator assembly encircling the array of coils. The actuator assembly, which includes a stack of ring magnets made of a permanent magnetic material, is arranged to move back and forth along the length of the array of coils under the control of signals that are applied to the coils. By applying appropriate drive signals to coils within the array, the position and movement of the actuator assembly along the linear array of coils and the force that the actuator assembly exerts can be controlled.
Linear actuators have numerous industrial and consumer product applications. One popular use is in robotic systems in which they might function to control the movement of jointed arms or manipulators. The linear actuator can operate the jointed arm causing it to move an object from an initial position to another fixed position at a controllable speed and causing it to hold the object in the fixed position. Typically, however, holding the object in a fixed position requires the continuing supply of power to the linear actuator to enable it to resist the pull of gravity on the object. If the power is interrupted, the linear actuator relaxes and gravity pulls the object down. As a consequence, when the source of power is limited, such as in the case of batteries, having to hold the object in its fixed position will drain power from the battery.
Thus, it is desirable to provide a mechanism that can be used to, among other things, hold the actuator assembly in a fixed position and eliminate, or at least reduce, the drain on the power supply.